Currently, soccer is one of the most popular sports in the U.S. with girls participating in this sport in increasing numbers. As several studies have documented that female youth soccer players have a higher rate of injury compared to male youth players, a prospective study of this young population is needed to determine injury incidence rates of recreational and elite soccer players as well as risk factors that predispose some girls to soccer injuries. Few investigators have performed prospective studies to evaluate female youth soccer players of middle school age, regardless of skill level. In addition, little research has evaluated the risk factors that are associated with the increased risk of injury among girls. Prior studies of several potentially important risk factors for soccer injuries including lower extremity muscle strength and limb alignment during jumping and landing (known as jump biomechanics) have been performed in older soccer players and some have noted conflicting results. We propose to perform a feasibility study to develop methodologies for ascertaining injuries and assessing several important injury risk factors among female youth soccer player's ages 12 to 14 years. Our specific aims are 1) to develop a prospective methodology for determining the incidence rate of soccer injuries in female youth ages 12 to 14 years who play on recreational and elite soccer club teams; 2) to estimate the reliability of measurements of lower extremity muscle strength, specifically hip flexion, extension, abduction, and adduction and the hamstring to quadriceps ratio of muscle strength; and 3) to estimate the reliability of measures of jump biomechanics. We will conduct a one-year, prospective, community-based cohort study of four recreational and four elite soccer teams in a Seattle area youth soccer association. We will assess injury ascertainment by comparing weekly team visits by an athletic trainer to weekly email questionnaires to parents. We will also determine inter-rater and intra-rater reliability of physical therapists that will measure muscle strength at the hip and knee and jump biomechanics. Findings from this research will be used to for the development of a large, prospective cohort study to evaluate potentially modifiable risk factors for injury among female youth soccer players. [unreadable] [unreadable]